Fast Plumbing Answers: Tankless Water Heater Making Noise?

You stepped into a hot shower and hear a knocking noise. Every time you use the dishwasher, the tankless water heater gurgles. Some tankless noises are caused by mineral buildup, trapped air or a loose fan- but which sounds indicate which problems?

Don’t worry: we’ll answer all your questions in 2 minutes or less.

At Mother, our licensed plumbers are passionate about evolving plumbing technology. We research, install and repair tankless water heaters on a weekly basis for homeowners in Dallas- one of the country’s toughest hard water regions on tankless systems. We know the difference between buzzing, humming and knocking- and how to fix each issue, fast.

Most tankless water heater noises are rumbling and popping caused by mineral buildup on internal components or your inlet filter. Whistling is caused by blocked ventilation, while a humming or buzzing noise means there’s a loose fan or internal component.

Need a quick tankless water heater fix in Dallas? Call Mother 24/7- we’ll have a plumber there within 24 hours to get your hot water back up and running.

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Most Tankless Noises Are Caused by Mineral Scaling

“Most noisy water heaters are caused by mineral buildup from hard water,” says our Master Plumber Jesse Crane.

Hard water is just as disruptive to tankless water heaters as conventional units. You don’t need a tank for mineral scaling to take its toll- calcium and limescale buildup clog inlet filters, build up on your tankless ignition components and other internal parts.

If you hear rumbling, popping or high-pitched whining from your tankless system, you probably need to have your unit descaled.

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Other culprits: loose internal components or water hammers

Loose internal components cause more mechanical-sounding noises- like humming or buzzing. If it sounds like a malfunctioning appliance, there’s probably a loose fan or component inside your tankless.

In less common circumstances, a water hammer creates a loud banging or knocking sound. This happens when water flow is restricted, causing the shock of sudden water pressure changes.

7 Common Tankless Water Heater Noises- And What They Mean

We asked Jesse to describe the most common noise complaints that homeowners have about tankless water heater systems. 

Then, he paired each noise with the most likely reason it’s happening.

Tankless water heater popping

The reason: Mineral buildup

Just like scaling in a conventional water heater, hard minerals like calcium and magnesium form deposits inside your tankless system over time. The popping noise you hear is loose minerals reacting to water heating up and rattling around your tankless.

Tankless water heater rumbling

The reason: Mineral buildup

Rumbling is another sound that internal scale buildup makes within a tankless. Where popping noises indicate some scale may have jarred loose, rumbling indicates large deposits stuck to internal components.

Scale buildup messing with your hot water delivery? Check out our fast guide to why your tankless isn’t producing hot water.

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Tankless water heater gurgling

The reason: Trapped air

Think about trapped air in any system- from a kettle to your own body. It causes gurgling noises within a pressurized area, especially when liquid (like water) is present. Gurgling noises are a telltale sign that your tankless system is housing trapped air.

Tankless water heater buzzing

The reason: Loose fan

When a standing fan or ceiling fan is loose, it buzzes or hums. The same thing happens to the fan inside your tankless system. If the fan is tight, then another internal component has jarred loose within the unit.

Tankless water heater knocking

The reason: Water hammer (water pressure changes)

A water hammer is what happens when water flow is suddenly stopped. This causes a shockwave in a pressurized water system- which is usually quite fast moving. This shock emits vibrations that make thumping sounds in your pipes.

Tankless water heater banging

The reason: Blocked vent

If the air ventilation on your tankless is blocked, you’ll hear a loud banging noise from the system. This happens when your vent is misaligned (poorly installed), or partially blocked by debris or a bird’s nest.

Tankless water heater whining

The reason: Sediment and mineral buildup

In this case, the noise is likely due to mineral and sediment buildup on your tankless water heater’s inlet filter. A blocked or clogged filter doesn’t let as much water pass through- the backed-up water increases in pressure, which causes the whining noise you hear.

Is your tankless water heater beeping, too? Find out what the beeping alarm means- and what every error code means on your Rinnai, Rheem or Navien tankless.

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How to Fix a Noisy Tankless Water Heater

Regardless of what’s causing the noise, Jesse advises you to call a licensed plumber to handle any inspection or repairs of your tankless water heater.

“You’re going to have to open the tankless up,” he says. “DIYers and homeowners can void their product warranty trying to work on internal parts themselves.”

The best course of action for your plumber depends on the reason for the noise coming from your system:

Descaling your tankless water heater

If your noisy tankless is due to mineral accumulation or sediment buildup, you’ll need to have it descaled. This is a common maintenance task that should be performed at least once a year to keep your tankless working as efficiently as possible.

Annual descaling allows homeowners to maximize the potential energy and utility bill savings their tankless can provide.

Hate descaling your tankless? Read our new article- we’ll cover three ways to stop descaling your water heater for good!

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Internal tankless repairs

If there’s a loose fan or internal component in your tankless, a licensed plumber easily handles that repair in a single appointment.

Your plumber will use a multimeter tool to diagnose the precise location of a more complex internal issue.

Vent blockage

Make sure you hire a licensed plumber if you suspect a blocked vent in your tankless system. They may have to access the vent on your roof to clean it out completely.

Water hammer issues

Your plumber may install a water hammer arrestor to correct any recurring water hammer issues.

These devices absorb the shock caused by changes in water pressure within the pipe leading to your tankless water heater. Not only will it stop the noises, it prevents cumulative long-term damage to your pipes and tankless unit.

Call Mother for Dallas Tankless Water Heater Repair

Most noises coming from your tankless water heater are caused by scale accumulation of hard water minerals in your inlet filter or internal components. Banging noises are caused by blocked air vents or water pressure shifts in your pipes, and buzzing noises mean a loose fan.

Whatever the reason for your noisy tankless, hire a licensed plumber to handle the diagnostics and repairs. Don’t risk voiding your product or manufacturer’s warranty by taking your tankless apart on your own.

Need tankless repair in Dallas? Mother’s here 24/7 to answer your call- trust our licensed pros for fast, lasting relief for all your water heater problems.

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